There is known an optometric apparatus constituted so that ocular refractivity of the right and left eyes of an examinee can be measured at the same time subjectively and objectively (See Japanese Patent Laid-Open No. 2000-83900).
This conventional optometric apparatus is so constituted that the examinee takes optometry following instructions of an optometrist.
However, optometric measurement of the examinee by the optometrist is not favorable in view of efficient management and cost reduction.
Also, recently, in the case of accommodative functional disorder such as near-vision disorder, asthenopia, sense of blear, etc. or in the case that abnormality of convergence and accommodation systems are suspected, when carrying out prescription of spectacles for reading or health management of VDT (video display terminal) workers and so on, accommodative functions such as accommodative near point, accommodative ability and accommodative dynamics are measured. For measurement of accommodative functions, subjective methods such as Ishihara's near point meter and accommodo-poly-recorder and objective methods such as infrared optometer and front-open type infrared optometer are used.
For measurement of subjective accommodative near point, 0.6 Landolt-ring targets and bar targets on near-distance optotypes are usually made to approach from the distance where an examinee can see the clearest at a constant rate of a target moving speed of 2.5 cm/sec to 5 cm/sec, and the distance where occurrence of even a slight blur is sensed is recorded as a near point.
The infrared optometer of the objective method has renovated a normal autorefractometer, in which an ocular refractive state of horizontal meridians when a target is moved at a constant speed is continuously measured so as to record dynamic characteristics of accommodation. The front-open type optometer records accommodation change of both eyes by moving a real space in front of the eyes with the target as an external target in the state close to natural vision.
However, in the subjective measurement of accommodative near point, after an examinee has learned blur of targets and subjective sensing standard of clear vision by practice, a distance where blur is sensed when a target is moved from a long distance to a short distance (disappearance threshold) and a distance where clear vision is enabled when the target is moved from the short distance to the long distance on the contrary (appearance threshold) are measured 3 times, respectively, and an average value of the both is set as a near point.
The measurement depends on subjective response and is subject to large fluctuation due to instability in subjective sensing standard between blur and clear visions of targets and uncertainty in target following motion and response of the examinee, which is particularly unsuitable for measurement of infants.
The measurement by the infrared optometer is carried out with one eye shielded and a target moved on the optical axis of one eye as accommodation stimulation, and it is different from daily relations between convergence and accommodation.
Accommodation and convergence are increased/decreased together in the daily life and in an unseparable relation with each other. Accommodation measurement with one eye shielded has a problem that accurate measurement of accommodative near point and accommodative ability is not possible.
With the measurement by the front-open type infrared optometer, external targets are utilized to present targets in the state closer to the natural vision, but it has a problem that a range of target movement is restricted and accommodative near point including far point can not be measured.
The present invention has been made in view of the above circumstances and its object is to provide an optometric apparatus which enables optometric measurement by an examinee himself/herself or an optometric assistant with less experience.
Also, an object of the present invention is to provide an optometric apparatus which presents targets to both eyes while maintaining the relation between accommodation and convergence, capable of measurement of accommodative functions in a wide target moving range, maintains the relation between accommodation stimulation and convergence constant, capable of easy measurement of accommodation regardless of refraction error of an examinee, and is suitable for diagnosis of cases such as near-vision disorder, asthenopia, blear, etc. and suspected abnormality in convergence and accommodation systems in the clinical ophthalmology as well as judgment when carrying out prescription of spectacles for reading and health management of VDT (video display terminal) workers, especially an optometric apparatus which can easily measure the relation between accommodation and convergence.